A gas turbine engine comprises a turbine and a compressor driven by the turbine, the compressor may be of an axial flow type. Commonly, the gas turbine engine is subjected to varying operating conditions resulting in different aerodynamic flow conditions within the compressor. In order to adapt the compressor performance to different operating demands, it is known to provide the compressor with variable guide vanes (VGV). The variable guide vanes are to be pivoted about their longitudinal axis in order to adjust their angle of attack.
Each variable guide vane is provided with a journal at its root, wherein the journal is pivot-mounted in a through hole in the compressor casing. The journal is accessible from outside the compressor casing and comprises a lever to be actuated for pivoting the variable guide vane. All levers may typically be coupled by means of a unison ring arranged concentrically around the compressor casing. The rotation of the unison ring actuates each of the variable guide vane levers of one stage simultaneously to achieve a corresponding rotational setting of each variable guide vane within the compressor casing.
An axial compressor consists of multiple stages of stator vanes and rotor blades. The front stages of stator vanes often have variable pitch to control the flow. Flow control is important on engine run up to avoid surge. Variable guide vanes of different stages may be pivoted by different angles.
It is known—and also shown in FIGS. 1 and 2—that individual vane pitch or angular offset is controlled via a linkage mechanism comprising vanes 10, 11 mounted on spindles 22 to allow angular movement of the vane 10, 11 and levers 20 for connecting the spindles 22 to a driving ring 40, 41, 42, 43, the so called unison ring, wherein all vanes 10, 11 in a single stage connecting to the same ring. Each ring is rotated via a control rod 50 from a common shaft 61. The shaft 61 may be rotated via a hydraulic ram 60 and may be fixed rotably via bearings. All mentioned reference signs relate to the FIGS. 1 and 2.
To attach this mechanism to the casing of the compressor with the required stability, an implementation is known (see also FIG. 3), in which a longitudinal beam 90 possibly with welded mountings at its ends, is bolted to bearings 80, 81 for the shaft 61 and bolted to brackets 70, 71, the brackets 70, 71 being bolted to the compressor casing 2. This provides a good stability but may have disadvantages in regards of manufacturing costs and of fatigue of welds. Furthermore a relative thermal expansion of the casing 2 has to be accommodated. This may be possible by allowing flexing of one the brackets 71. This flexibility is indicated in FIG. 3 by showing a lesser width of the bracket 71 compared to the other bracket 70.
According to EP 1 101 902 A2, a torque shaft assembly includes a hollow tube with a central axis disposed between and fixedly connected to first and second crankshafts at first and second distal ends. This shaft specifically is adapted to vibrations of the engine during operation, as a hollow interior of tube between the first and second crankshafts is filled with a sufficient quantity of flowable inertia material or damping media to absorb vibratory energy by friction during operation of the engine. The shaft may provide the needed stiffness such that an additional beam between the first and the second distal ends is not necessary. The first end shaft is rotatably supported by a first shaft bearing which is preferably a lined journal bearing type. The second end shaft is rotatably supported by a second shaft bearing which is preferably a spherical bearing.
In EP 2 136 036 A1 a crank shaft is disclosed that is comprised of first and second crankshafts and a torsion bar connected to both crankshafts. An additional longitudinal beam, as discussed above, is not part of this control mechanism.
According to DE 18 05 942 A1, a crank shaft is disclosed with two studs for which “self-adjusting” bearings may be provided to allow easy assembly.